系统当前时间是多少周，就是是今年的第几个星期
select to_char(sysdate,'ww') ,to_char(sysdate,'iw') from dual;
select to_char(sysdate,'ddd') from dual;
select TRUNC(SYSDATE,'MM') from dual;1）
ww的算法为每年1月1日为第一周开始，date+6为每一周结尾
例如:20050101为第一周的第一天，而第一周的最后一天为20050101+6=20050107
公式: 每周第一天 ：date + 周 * 7 - 7 每周最后一天：date + 周 * 7 - 12）
iw的算法为星期一至星期日算一周，且每年的第一个星期一为第一周，
例如:20050101为星期六，所以用iw的算法是前年的53周，而20050103之后才是第一周的开始。
公式: 每周第一天 ：next_day(date) + 周 * 7 - 7每周最后一天：next_day(date) + 周 * 7 - 13）
其它：
A、查今天是 "本月" 的第几周 SELECT TO_CHAR(SYSDATE,'WW') - TO_CHAR(TRUNC(SYSDATE,'MM'),'WW') + 1 AS "weekOfMon" from dual; 或 SELECT TO_CHAR(SYSDATE,'W') AS "weekOfMon" from dual;
B、查今天是 "今年" 的第几周 select to_char(sysdate,'ww') from dual; 或 select to_char(sysdate,'iw') from dual;
统计哪年哪个星期的哪一天：
int year=2011;
int week=1;
Calendar calFirstDayOfTheYear = new GregorianCalendar(year,
Calendar.JANUARY, 1);
calFirstDayOfTheYear.add(Calendar.DATE, 7 * (week-1));
int dayOfWeek = calFirstDayOfTheYear.get(Calendar.DAY_OF_WEEK);
Calendar calFirstDayInWeek = (Calendar)calFirstDayOfTheYear.clone();
calFirstDayInWeek.add(Calendar.DATE,
calFirstDayOfTheYear.getActualMinimum(Calendar.DAY_OF_WEEK) - dayOfWeek);
Date firstDayInWeek = calFirstDayInWeek.getTime();
System.out.println(year + "年第" + week + "个礼拜的第一天是" + ReportDateUtil.getFromatDay().format(firstDayInWeek));
Calendar calLastDayInWeek = (Calendar)calFirstDayOfTheYear.clone();
calLastDayInWeek.add(Calendar.DATE,
calFirstDayOfTheYear.getActualMaximum(Calendar.DAY_OF_WEEK) - dayOfWeek);
Date lastDayInWeek = calLastDayInWeek.getTime();
System.out.println(year + "年第" + week + "个礼拜的最后一天是" + ReportDateUtil.getFromatDay().format(lastDayInWeek));